Nucleolar dominance is a stable epigenetic phenomenon by which the rRNA genes of one parent are transcriptionally repressed in an F1 hybrid. Nucleolar dominance in hybrid cells is thought to be an extreme extension by which the non-hybrid cell may control the extant of ribosomal gene transcription. As an epigenetic process it is an attractive model for several reasons, most importantly it is completely reproducible, second, it is a general process that occurs through a broad range of plants and animals, finally, the processes that regulate transcription of rRNA genes are likely to play a transcriptional role genome wide. Dr. Pikaard's lab has extensive experience in investigating nucleolar dominance, additionally, in an NSF sponsored collaboration with a consortium of other labs, the Pikaard lab is now completing a two-year project in knocking out all of the known chromatin modifying genes in Arabidopsis. This greatly expands the tools by which I can begin studying this process. My specific aims are to first identify genes that are involved in the process of establishing nucleolar dominance. I have started screening our collection of knockouts as well as creating novel mutants disrupted in their ability to induce nucleolar dominance. With these mutants in hand I will then be able to investigate the physical and genetic interactions between these genes. Finally, given the rapid advances in our analysis of chromatin structure, I will be able to examine how chromatin modification drives transcriptional silencing.